﻿//岛屿数量（medium):https://leetcode.cn/problems/number-of-islands/description/
class Solution {
public:
    int ret;
    int n,m;
    bool vis[310][310];
    int dx[4] = {0, 0, -1, 1};
    int dy[4] = {1, -1, 0, 0};
    int numIslands(vector<vector<char>>& grid) {
        m=grid.size(),n=grid[0].size();
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(!vis[i][j]&&grid[i][j]=='1')
                {
                    vis[i][j]=true;
                    dfs(grid,i,j);
                    ret++;
                }
            }
        }
        return ret;
    }
    void dfs(vector<vector<char>>& grid,int i,int j)
    {
        for(int k=0;k<4;k++)
        {
            int x=i+dx[k];   int y=j+dy[k];
            if(x>=0&&x<m&&y>=0&&y<n && !vis[x][y] &&grid[x][y]=='1')
            {
                vis[x][y]=true;
                dfs(grid,x,y);
            }
        }
    }
};

//岛屿的最大面积(medium): https://leetcode.cn/problems/max-area-of-island/
class Solution {
public:
    int ret;
    int MaxRet;
    int m,n;
    bool vis[55][55];
    int dx[4] = {0, 0, -1, 1};
    int dy[4] = {1, -1, 0, 0};
    int maxAreaOfIsland(vector<vector<int>>& grid) {
        m=grid.size(),n=grid[0].size();
        for(int i=0;i<m;i++)
        {
            for(int j=0;j<n;j++)
            {
                if(!vis[i][j]&&grid[i][j]==1)
                {
                    ret=1;
                    vis[i][j]=true;
                    dfs(grid,i,j);
                    MaxRet=MaxRet<ret?ret:MaxRet;
                }
            }
        }
        return MaxRet;
    }

    void dfs(vector<vector<int>>& grid,int i,int j)
    {
        for(int k=0;k<4;k++)
        {
            int x=i+dx[k];   int y=j+dy[k];
            if(x>=0&&x<m&&y>=0&&y<n && !vis[x][y] &&grid[x][y]==1)
            {
                vis[x][y]=true;
                ret++;
                dfs(grid,x,y);
            }
        }
    }
};